Recently the light-emitting diode (LED) becomes one of the solid state lighting sources having an extremely potential due to the epitaxy and process technology progress. LED can only be driven by direct current due to physical mechanism restriction, therefore the alternating current provided directly from the power plant is transferred to the direct-current used by LED in any lighting design for LED light source. The above electronic devices for rectification and voltage adjustment increase the cost and decrease the efficiency of the alternating current transfer to direct current, not mention to its big volume. The above disadvantages can influence the reliability and life-time of the LED used in illumination application in daily life.
ACLED devices do not need the electronics devices for rectification and/or voltage adjustment and can be directly operated under alternating current, so the ACLED devices are highly possible to be the mainstream products of the solid state lighting source in stationary position in the future.
Because of the current leakage, the luminous intensity of LED drops when the temperature is increased. To alleviate the current leakage problems, the carrier concentration of the p-type confining layer is usually increased, or a material with higher level energy gap material is grown to increase the confining ability of the electrons. In most situations, the increasing degree of the carrier concentration of the p-type confining layer is limited, and when the carrier concentration of the p-type confining layer is increased, the light emitting quality is affected because the higher carrier concentration forces the p-type carrier move towards the active layer which has lower carrier concentration.